Abstract: An infrared-absorbing mark printed matter in which an infrared-absorbing mark is formed on a substrate by printing with an ink having high light absorptivity in the infrared region; the infrared-absorbing mark is covered up by smearing with an ink having high light absorptivity in the visible region and pervious to light in the infrared region to form a colored concealing layer; and on the colored concealing layer is formed a white concealing layer by printing with an ink containing a white pigment and an extender pigment of which at least part of the particles are those having an average particle size of 3 to 20 .mu.m.

Abstract: A magnetic recording medium having two magnetic layers, which comprises an upper magnetic layer and a lower magnetic layer, said lower magnetic layer having a coercive force of at least 100 oersteds, preferably 100 to 500 oersteds, lower than that of the upper magnetic layer, the thickness of the upper and lower magnetic layers being in the ratio of the thickness of the upper magnetic layer to that of the lower magnetic layer of 1/1 to 1/9, and the total coercive force of the upper and lower magnetic layers being 1,000 oersteds or more. The magnetic recording medium has excellent sensitivity and frequency characteristics at low and high frequency bands with less noise.

Abstract: A magnetic recording medium suitable for high-density recording which comprises a substrate and a magnetic layer thereon, the magnetic layer containing acicular magnetic metal particles having a particle size of not more than 0.3.mu. and a squareness ratio in the vertical direction of the layer being not less than 0.4.